Isometric exercise above but not below an individual’s pain threshold influences pain perception in people With lateral epicondylalgia

OBJECTIVE: To examine the acute effects of isometric exercise of different intensities on pain perception in individuals with chronic lateral epicondylalgia. METHODS: Participants performed three experimental tasks completed in a randomised order on separate days: control (no exercise) and isometric wrist extension (10 x 15 sec) at load 20% below (infra-threshold) and 20% above (supra-threshold) an individual’s pain threshold. Self-reported pain intensity (11-point numeric rating scales (NRS)), pressure pain threshold and pain free grip were assessed by a blinded examiner before, immediately after and 30min after task performance. Correlation between pain ratings and clinical variables, including pain and disability and kinesiophobia was performed. RESULTS: 24 individuals with unilateral lateral epicondylalgia of median 3-month duration participated. Pain intensity during contraction was significantly higher during supra-threshold exercise than infra-threshold exercise (Mean difference in NRS 1.0, 95%CI 0.4, 1.5, p = 0.002). Pain intensity during supra-threshold exercise was significantly correlated with pain and disability (R=0.435; p=0.034) and kinesiophobia (R=0.556, p=0.005). Pain intensity was significantly higher immediately after performance of supra-threshold exercise, compared to infra-threshold exercise (p=0.01) and control (p<0.001) conditions, while infra-threshold exercise and control conditions were comparable. Thirty minutes later, pain levels remained significantly higher for supra-threshold exercise compared to infra-threshold exercise (p=0.043). Pressure pain threshold and pain free grip showed no significant effects of time, condition, or time by condition (p>0.05). DISCUSSION: Individuals with lateral epicondylalgia demonstrated increased pain intensity following an acute bout of isometric exercise performed at an intensity above, but not below, their individual pain threshold. Further investigation is needed to determine whether measurement of an individual’s exercise induced pain threshold may be important in reducing symptom flares associated with exercise.